1. Field of the Invention
The present invention relates to an image forming apparatus, and, more particularly, to an image forming apparatus including a fusing device to fix a toner image to print media.
2. Description of the Related Art
An image forming apparatus is an apparatus that forms an image on print media, and may include, for example, a printer, a copier, a facsimile, a multifunctional machine integrating various functions, and the like.
An electro-photographic type image forming apparatus generally scans light on a photoconductor charged with a predetermined electric potential to form an electrostatic latent image on the surface of the photoconductor, and supplies toner to the latent image to develop into a visible toner image. The toner image, developed on the photoconductor, is transferred to print media, which is then fixed to the print media by passing the print media through a fusing device.
A widely used fusing device includes a heat roller having a heat source mounted therein and a press roller in pressing contact with the heat roller to form a fusing nip. When the print media, to which the toner image has been transferred, enters between the heat roller and the press roller, the toner image is fixed to the print media by the heat and pressure at the fusing nip.
The heat roller however due to its large heat capacity requires a significant warm up time to reach the temperature sufficient to carry out the fixing operation when, for example, the image forming apparatus is restarted from being idle for some time or is initially operated after being powered up.
In recent years, there has been suggested a fusing device that is capable of rapidly increasing the temperature of the nip to a sufficient temperature for fusing the toner in response to the demand for high-speed image forming apparatuses. An example of such fusing device is disclosed in United States Patent Application Publication No. US 2006/0177251 by Uehara et al. (“Uehara”).
The fusing device of Uehara includes a press roller, a fusing belt that rotates with the rotation of the press roller, a halogen heater mounted in the fusing belt to heat the fusing belt, and a belt guide member to support the inner circumference of the fusing belt and to form a fusing nip together with the press roller.
Some of heat produced by the halogen heater heats the belt guide member adjacent to the fusing nip, and the fusing belt is indirectly heated by heat transmitted from the heated belt guide member. Also, some of heat from the halogen heater directly heats the fusing belt at the side opposite to the fusing nip. Consequently, the fusing belt is heated to a predetermined temperature in a relatively short time by the halogen heater.
While these type of fusing devices described by Uehara may allow rapid heating of the fusing belt, and thus may reduce warm-up time when the device operates as intended, when the fusing device does not operate normally, however, the fusing belt may become damaged or accidents threatening safety may occur due to the overheating of the fusing belt.
For example, when the fusing belt does not rotate as it should, due to, e.g., a slippage between the press roller and the fusing belt or due to malfunctions in the drive system delivering rotational power to the press roller, etc., the temperature of the fusing belt at the parts where the fusing belt is directly heated by the halogen heater may rapidly increase, and may overheat, which may result in the fusing belt being damaged, and/or an occurrence of hazardous accident, such as a fire.